Catheters are used commonly in the diagnosis and treatment of a wide variety of medical conditions. A catheter typically is in the form of an elongate flexible tube adapted for insertion into the human body. In a typical procedure, the catheter is advanced and manipulated to place its distal end (the end inside the patient) at a target site in the body. The distal end of the catheter typically is constructed to perform a particular diagnostic or therapeutic procedure at that target site. For example, many catheterization procedures involve the insertion and advancement of a catheter into a patient's blood vessels. The catheter may be a diagnostic angiographic catheter intended to inject radiopaque contrast liquid into the patient's blood vessels so that they may be visualized under X-ray fluoroscopy or may be a therapeutic catheter such as a balloon angioplasty catheter in which a balloon at the distal end of the catheter is used to dilate a narrowed region of a blood vessel.
As an aid to advancement and placement of the catheter, specially constructed guidewires often are used. The guidewire may be inserted into the patient pre-assembled with the catheter or may be inserted into the patient independently of the catheter, with the catheter being threaded onto and advanced along the previously placed guidewire. In either case, the guidewire extends distally beyond the distal end of the catheter so that it may serve as a lead or guide for the catheter as the catheter is advanced. In order to place the distal end of the guidewire at the intended target site, the guidewire typically must be manipulated and steered through various branches of the patient's vasculature in order to reach the target site. For that purpose, it is common practice to provide a bend in the distal tip of the guidewire and to construct the guidewire so that it can transmit rotation from its proximal to its distal end. Thus, as the wire is advanced, it can be steered at branches in the vasculature by rotating it so that the bent distal tip is directed toward the intended blood vessel branch. By way of example, such guidewires are described in U.S. Pat. No. 4,545,390 (Leary). Some types of guidewires are provided with a means by which the shape of the curve at the distal end of the guidewire can be controllably adjusted from the proximal end of the guidewire without removing the guidewire from the patient. For example, U.S. Pat. Nos. 3,521,620 (Cook) and 4,719,924 (Crittenden) disclose such guidewires with controllably variable curved distal tips. Typically such guidewires include a pull wire that extends through the guidewire and is connected at its distal end to the distal tip of the guidewire. The degree to which the pull wire is pulled controls the degree of curve at the distal end of a guidewire. Such guidewires typically have a single pull wire and, therefore, can only be bent in one direction.
In some types of catheters, particularly those that are not intended to be used with a guidewire, it may be desirable to provide an adjustably curvable distal tip with control means by which the degree of curvature at the distal tip can be remotely controlled. Examples of such catheters are found, for example, in U.S. Pat. No. 4,753,223 (Brenner). Typically such catheters also use pull wires and may use a plurality of pull wires to control the direction of bending of the distal tip of the catheter. Such multiple pull wires are common in endoscopes. The use of multiple pull wires, however, requires that the diameter of the device be increased in order to accommodate the multiple pull wire arrangement. Some may use liquid pressure such as is disclosed in U.S. Pat. No. 3,773,034 (Burns et al.) to control the direction of the catheter tip.
A characteristic common to the foregoing steerable guidewires and catheters that is in order to steer and advance the device, it is necessary often to transmit torque along the length of the device, from its proximal to its distal end in order that the direction of the curve at the distal end may be controlled. In some cases, it is difficult to construct a device that will have sufficient torsional rigidity to transmit the rotation controllably, without whipping. It would be desirable, therefore, to provide a steering system for use in a guidewire or a catheter in which the distal tip of the catheter could be selectively directed within the patient's body with reduced reliance on the torsional capability of the device. It is among the general objects of the invention to provide such a device which incorporates a new approach for remotely controlling the curvature at the distal end of a guidewire or a catheter without requiring removal of the guidewire or catheter from the patient.